I was brainstorming in the shower the other day, and I thought “Eureka!” – I need to bootstrap and test my Java app on a dynamic cluster with 800 Tomcat servers right now! Then, breakfast.

Obviously, every now and then you need to build a dynamic cluster of 800 Tomcat machines and then run some tests. Oh, wait, you don’t? Well, lets say you do. Provisioning your machines on the cloud for testing is a great way to “exercise” your app and work on:

Leaving nothing behind: After you’ve got all green lights, shut it all down and watch it disappear

At ZeroTurnaround, we need this for testing LiveRebel with larger deployments. LiveRebel is a tool to manage JEE production and QA deployments and online updates. It is crucial that we support large clusters of machines. Testing such environments is not an easy task but luckily in 2012 it is not about buying 800 machines but only provisioning them in the cloud for some limited time. In this article I will walk you through setting up a dynamic Tomcat cluster and running some simple tests on them. (Quick note: When I started writing this article, we had only tested this out with 100 Tomcat machines, but since then we grew to be able to support 800 instances with LiveRebel and the other tools).

Technical Requirements

Let me define a bunch of non-functional requirements that I’ve thought up. The end result should have 800 Tomcat nodes, each configured with LiveRebel. A load balancer should sit in front of the nodes and provide a single URL for tests, and we’ll use the LiveRebel Command Center to manage our deployments.

Naturally, this is all easier said than done. The hurdles that we will need to overcome to achieve this are:

Configuring a load balancer (Apache) with all the provisioned IP addresses

Automation – one-click provision/start/stop/terminate on the cluster using Jenkins

Tools

We chose Amazon AWS as our cloud provider, namely because we’ve become familiar with them over the last couple years. For provisioning we use Knife and for configuration management we like Chef. For automation, we went with Jenkins (I love Jenkins), and we have two jobs. One to start the cluster and one to stop the cluster. Tests are not automated at the moment. Before going further you have to have a Chef server running on some machine (it should not be necessarily your own workstation) and Knife installed and configured on your Jenkins machine.

Architecture

Loadbalancer

First we have to create/launch a loadbalancer instance. Software to configure:

Install Apache

Install/enable Apache loadbalancer module

Update Apache configuration

Install LiveRebel Command Center and start it (could be a separate machine but we’ll use this instance for 2 services)

The load balancer should check in with chef-server and provide his own IP address. LiveRebel Command Center should be running and accepting incoming requests on default port (9001).

LiveRebel node(s)

As soon as the load balancer is ready we will create/launch nodes. Node instances need to:

Install a Tomcat instance

Figure out the IP of the load balancer

Download lr-agent-installer.jar from the LiveRebel CC

Run it (java -jar lr-agent-installer.jar)

Start Tomcat

Again, when everything is done the node will check in with chef-server and provide its IP address.

After all nodes are ready we must update the Apache load balancer configuration and provide all the IP addresses of the nodes. This is because of the architecture of the load balancer. It needs to know the IP addresses of the machines it balances.

Code (The Fun Part)

As we are using Chef, the natural way to act is to create several cookbooks and a couple of roles, that will help us with configuration. There are four cookbooks in total, one for each application: Apache, lrcc, Tomcat and Java. You can get familiar with them on Github. The code is provided more just for information, because it will not run as is. There are some download links missing. Another thing is that it was tested only on Ubuntu, so if you are using some other distribution, you may need to tune it up.

We are going to use Knife command line tool to start and bootstrap our instances. Don’t forget to install and configure Knife-EC2 rubygem. First step is to create the load balancer. Provided you have configured the Knife EC2 plugin and prepared the right AMI to launch (or use the default provided by Ubuntu) it is relatively easy, just run (with right parameters):

When the process finishes successfully you can go to https://your-server-address:9001/ and check if the LiveRebel is running. It should be, but you will have to register or provide a license file. If you already have a license file you can automate the registration step by copying the license into LiveRebel home folder in your cookbook. Another thing to check is – if the load balancer has registered with chef-server.

Next step – creating lr-nodes. Your 800 nodes can be created using a similar Knife EC2 command run in loop:

Everything is almost ready! All we need now is to create Jenkins jobs. The first one – we’ll name it lr-cluster-create – should run these 2 commands and start the cluster. And the other one lr-cluster-delete – stops it with these commands:

Conclusions

At this point, you should be well on your way towards bootstrapping a clean environment, installing, running your tests, checking load handling, and then you can shut it all down once you’ve seen everything working to your satisfaction.

Your two Jenkins jobs are now able to spawn a dynamic Tomcat cluster. You can even parameterize your job and supply a number of nodes that you are interested in for a really dynamic cluster.

One thing to note is that as in EC2, Amazon charges for EBS snapshots, so it is not very cost-effective to just stop the cluster. Termination here will save you some money, especially if you like bigger clusters.

Another thing is provisioning. Parallel provisioning for the 800 nodes takes roughly 30 minutes. Starting a new instance from AMI takes some time, but most of it goes to bootstrapping the clean environment with the Chef installation and downloading packages and archives.

Once you have the cluster started you still need to run tests. We test deploying, updating the whole cluster with LiveRebel. You could be testing your own WEB application and see how it handles the load.

The next steps for us is to automate the test suite and have these large scales tests executed regularly. This will give us valuable feedback about releases in progress and their scalability.

I hope this article has helped you get started with dynamic Tomcat clusters and I’m more than happy to go into more detail about any step here if you have questions – you can reach me at juri.timosin@zeroturnaround.com.

A former Ruby on Rails and C#.Net developer, he switched to providing infrastructure support using DevOps methodologies with Chef and Jenkins. Juri likes Ubuntu, playing football, chess and snooker, swimming and cycling. He is fond of interesting and difficult programming problems, takes part in competitions (such as code jam and AI contest), and sometimes writes about it in his blog. You can connect to Juri via LinkedIn or follow on Google+.

to speed process up you can prepare and register your custom AMIs so
provisioning does not take 30 minutes. You can also script this process
and build custom AMIs daily or whenever your base provisioning script
change.